1. Technical Field
The invention relates to an electrophotographic photoreceptor, a process cartridge, an image forming apparatus, and a coating composition used for the electrophotographic photoreceptor.
2. Related Art
Generally, an electrophotographic image forming apparatus has the following structure and processes. Specifically, the surface of an electrophotographic photoreceptor is uniformly charged by a charging means to desired polarity and potential, and the charged surface of the electrophotographic photoreceptor is selectively removed of charge by subjecting to image-wise exposure to form an electrostatic latent image. The latent image is then developed into a toner image by attaching a toner to the electrostatic latent image by a developing means, and the toner image is transferred to an image-receiving medium by a transfer means, then the image-receiving medium is discharged as an image formed material.
Electrophotographic photoreceptors are currently been widely used in the field of copying machines, laser beam printers and other apparatus due to advantages of high speed and high printing quality. As electrophotographic photoreceptors used in image forming apparatus, organic photoreceptors using organic photoconductive materials are mainly used which are superior in cost efficiency, manufacturability and disposability, compared to conventionally used electrophotographic photoreceptors using inorganic photoconductive materials such as selenium, selenium-tellurium alloy, selenium-arsenic alloy and cadmium sulfide.
As a charging method, a corona charging method utilizing a corona charging device has been conventionally used. However, a contact charging method having advantages such as low ozone production and low electricity consumption has recently been put into practical used and is widely used. In the contact charging method, the surface of a photoreceptor is charged by bringing a conductive member as a charging member into contact with, or in close proximity to, the surface of the photoreceptor, and applying a voltage to the charging member. There are two methods of applying a voltage to the charging member: a direct current method in which only a direct current voltage is applied, and an alternating current superimposition method in which a direct current voltage superimposed by an alternating current voltage is applied. The contact charging method has advantages of downsizing the apparatus and suppressing generation of harmful gases such as ozone, but at the same time has disadvantages of being easily degraded and worn due to a direct charging on the surface of a photoreceptor.
As a transfer method, a method of transferring directly to a paper has conventionally been the mainstream. However, a method of transferring to a paper via an intermediate transfer body, in which a wider variety of paper can be used, is currently frequently used.
In conducting direct charging or using an intermediate transfer body, there can be a problem of damaging or stabbing of a photoreceptor due to foreign matter involved in an image forming apparatus and pinched between an intermediate transfer body and a photoreceptor, thereby easily causing a photoreceptor leak (a local flow of an excessive current through a photoreceptor). Problems such as a photoreceptor leak also tend to be aggravated by the intensified abrasion which occurs in the direct charging.
To overcome such problems, there has been proposed a way to enhance the strength of the photoreceptor by providing a protective layer on the surface of an electrophotographic photoreceptor.
A protective layer using a phenolic resin is superior in producing a stable image over the long-term because of its high gas barrier property and high resistance against strong oxidizing gases such as discharge products.
However, the phenolic resin has had serious problems such as significantly low adhesiveness to the underlying charge transporting layer due to a great degree of volumetric shrinkage during curing, intense occurrence of ghosts during repeated image forming which may be caused by microvoids being generated between the protective layer and the charge transporting layer due to poor adhesiveness of the phenolic resins, and unstable potential characteristics.